This document discusses interchangeable manufacture, terminology for limits and fits. It defines interchangeable manufacture as parts that are identical enough to be mutually interchangeable in any device of the same type. It provides examples like bottle caps, rims, tires. The advantages are easy replacement, assembly, repair by minimizing time and cost.
It then defines terminology for limits and fits, including basic size, tolerance, allowance, deviations, fits. It explains hole basis and shaft basis systems for defining limits and fits between holes and shafts to achieve clearances, interference or transition fits.
2. Interchangeable Manufacture
Definition
The interchangeable manufacture implies that,
the parts that are for practical purposes
identical. They are made to specifications by
processes that ensure that they are so nearly
identical that they will fit into any device of the
same type
4. Advantages For Interchangeable
Manufacture
Replacement: One such part can freely replace
another, without any custom fitting (such
as filling).
Easy to Assembly: This interchangeability
allows easy assembly of new devices
Repairing: Easier repair of existing devices.
Minimizing time and cost :Minimizing both the
time and skill required of the person doing the
assembly or repair.
Rapid Manufacturing :Machine tool enables the
components to be manufactured more rapidly
5. Terminology for LIMITS & FITS
Terminology:- The terms related to limit system are as
below:
Size:- It is a number expressed
in a particular unit in the
measurement of length.
Basic Size
Basic Size:- It is the size based
Hole
Shaft on which the dimensional
deviations are given.
Actual Size:- It is the size of the component by actual
measurement after it is manufactured. It should lie
between the two limits of size.
6. Terminology for Limits and Fits Cont.
Limits of size:- These are the maximum and minimum
permissible sizes of the part.
Maximum limit:- Is the maximum size permitted for the part.
Minimum limit:- it is the minimum size permitted for the part
limit of size.
Hole:-Refers to diameter of a circular
hole as well as to any internal dimension
of component .it is referred as “female”
Basic
Hole
size
Shaft
Shaft:-Limits and fits, all external features of a component
including those which are not cylindrical are designated as
‘Shaft'. It is referred as “male”
7. Terminology for Limits and Fits Cont.
Tolerance :Tolerance is the difference between maximum limit of size and
minimum limit of size.
Tolerance
zone
Upper limit = 28 . 2
Zero line
Lower limit = 27. 8
Ø28 0.2
(Basic)
Hole
8. Allowance
It is an intentional difference between the
maximum material limits of mating parts,
For shaft, the maximum material will be it’s
high limit and for hole, it will it’s low limit
9. Different Types of limit
Unilateral Limit: In this
method of presenting the
limits, both the limits of size
are on the same side of the
zero line.
Bilateral Limits: Here one Zero line
of the limits is on one side of
the zero line And the other
limit of size is on the other
side of the line.
10. Deviations
Upper Deviation
Lower Deviation
Deviation:- It is the algebraic
difference between a size, to its
corresponding basic size. It may be
positive, negative or zero.
Hole
Upper Deviation:- It is the
Max.dia.
Min.dia.
Max.dia.
Min.dia.
Shaft algebraic difference between
maximum limit of size and its
corresponding basic size.
Lower Deviation:- It is the algebraic difference between
minimum limit of size and its corresponding basic size.
Actual Deviation:- It is the algebraic difference
between actual size and its corresponding basic size.
11. Fit
Fit is the relationship that exists between two mating parts, a
hole and shaft with respect to their dimensional difference before
assembly. Three types of fit are given hereunder;
Clearance Fit : In clearance Fit shaft is
always smaller than the hole. A positive
allowance exists between the largest
possible shaft and smallest possible hole.
Minimum Clearance : It is the
difference between the
maximum size of shaft and Hole basis
minimum size of hole.
Maximum clearance: It is the
difference between the
minimum size of the shaft and
the maximum size of hole
Shaft Basis
12. Fit Cont.
Interference Fit: It is also
called Press or force fit, In
this fit shaft is always
larger than the hole
Minimum interference: it is the
difference between the
maximum size of hole and the
minimum size of shaft prior to Shaft
assembly Hole
Minimum Interference: It is the
difference between the
minimum size of the hole and
the maximum size of the
shaft prior to assembly.
13. Fit Cont.
Transition Fit: it is called sliding
Fit . It occurs when the resulting
fit due to the variations in size
of the male and female
components due to their
tolerance, varies between Shaft
Hole
clearance and interference fits.
The tolerance zones of shaft
and hole overlap
14. Hole Basis System Shaft Basis System
Hole is keep constant and the shaft Shaft is kept constant and the hole diameter
diameter is varied is varied.
The basic size of the hole is taken as The basic size of the shaft is taken as one of
the low limit the limits(maximum) of size of shaft
The high limit of the size of the hole The other limit of size of the shaft and the
and the two limits of size of the shaft two limits of hole are then selected to give
are selected to give the desired fit the desired fit
The actual size of the hole is within The actual size of a hole that is within the
the tolerance limit. tolerance limits is always less than the basic
In this system Hole gets the letter H size.
and the shaft gets letter o decide the In this system Shaft gets the letter h and the
position of tolerance hole gets different letter o decide the position
of the tolerance zone to obtain desired fit
